SC2 seems to limit you to the one character name (and with that 3 digit friend code it is used for in-SC2 friends without the bond a RealID link creates - hence our use of it here) and I suspect that is the name you'll post under in the official forums (WoW lets you select any of your characters to post as, but SC2 says you'll only have the one shot at a profile name when you first log in).